Stents are fine, cylindrical pieces of wire mesh, which are introduced into arteries in which deposits have formed. A balloon catheter is then used to expand the stent at the narrowed point of the artery. After the catheter is removed, the stent serves as a vascular support, which keeps the artery open. Depending on the individual situation and the area of application, stents can be designed in different ways, different sizes, and can be made of different materials, including their coatings.
Cardiovascular stents must meet stringent requirements to ensure that they will function properly. If the stent has rough or sharp edges, it can damage blood cells or the blood vessels into which they are inserted. This can lead to further rupture of the atherosclerotic plaque, embolisms, and blood clots, which can lead in turn to potentially life-threatening situations.
The present invention pertains to a device for illuminating and inspecting stents and other similar parts which have the form of small, precision-made tubes.
Lasers are usually used to cut or weld stents. Although highly precise, such a method can occasionally lead to defective parts. Stents are relatively small with diameters of only about 1 mm. After processing, the individually cut features on a stent range from 50 to 200 μm in size. Accordingly, small changes in the process parameters such as the laser power, tube diameter, etc, can cause defects. Such defects can include a feature having a size that is out-of-tolerance or a feature that is malformed.
Because stents are used in the heart or in other critical areas of the circulatory system, a malfunction of the stent can be life-threatening. The production of stents therefore typically includes inspection measures. Normally, a human operator examines the stents under a stereo microscope to determine if there are any visible defects. The cylindrical stent is rotated by means of an appropriate mechanical device, and the operator inspects both the inside and the outside of the stent, section by section. Typical defects include, for example, deviations of the stent structures from the nominal dimensions and various kinds of surface defects, such as contamination, scratches, sharp points, etc., the elimination of which are absolutely critical to the safe functioning of the stent. A multi-dimensional inspection is typically conducted by a human operator with the use of a profile projector. Alternatively, this examination can also be conducted automatically using an image processing system.
Many problems are associated with such manual and automatic inspection methods. First, human error makes the visual inspection of products less effective. Second, manual inspection is relatively slow and, thus, represents a relatively expensive side of the production process. Furthermore, a typical profile projector used for manual inspection does not usually supply numerical dimensional data, which could be important under certain conditions for process control. In addition, when the outer and inner surfaces of the stent are examined, typically both surfaces are illuminated simultaneously. This leads to reflections, which prevent automatic inspection.
JP 2001066521 A describes a method and a device for inspecting the inside surface of a (coated) stent, according to which the stent is pushed onto a so-called “fiber scope”. The inspection is conducted visually by an observer. It is therefore not automated. However, there is nothing in this publication with respect to how the stent is illuminated.
JP 2001070455 A discloses a method for inspecting the pattern width on the surface of the stent. The recorded image of the stent is compared with previously entered reference data.
This document also fails to provide any information on how the stent is illuminated.
JP 2001074433 A describes a method and a device similar to JP 2001070455 A for inspecting the outside surface of a stent. No illumination is provided for the stent during inspection.
Lastly, U.S. Pat. No. 6,606,403 B2 discloses an automatic system for illuminating, inspecting, and measuring stents and other small, precision-cut tubes and components. The system disclosed therein consists of a linear array electronic camera with a lens; a light source for providing the necessary illumination; a mandrel onto which the tube is mounted during the inspection; a rotating stage for rotating the mandrel; and a computer-based electronic image-recognition system, which creates a line-by-line image of the stent as it rotates under the camera. This system, however, can only be used to inspect the outside surface of the stent.